This project is concerned with the nature and clinical consequences of antibiotic tolerance in strains of Staphylococcus aureus. These organisms are present in 30-50% of all blood cultures from hospitalized patients with S. aureus bacteremia and in some cases these organisms have been shown to persist despite treatment with antibiotics. Tolerant staphylococci are inhibited by penicillinase-resistant derivatives of benzylpenicillin and other cell wall active antibiotics, but the cells are not killed by these drugs. This investigation will attempt to ascertain the relationship of lipoteichoic acid excretion to this antibiotic tolerance since this material has been implicated as an inhibitor of autolysin activity in other organisms. In addition, we will use isogenic substrains of S. aureus, which have been shown to differ in their relative susceptibility to killing by penicillins, to establish the biochemical basis for the observation that tolerant staphylococci survive in normal granulocytes longer than non-tolerant cells. We will challenge normal, isolated polymorphonuclear leukocytes with tol plus and tol minus cells and measure metabolic stimulation of the granulocytes (oxygen uptake and glucose metabolism), H2O2-myeloperoxidase iodination potential, superoxide (O2 minus) production, and using extracts of normal PMN leukocytes, we will ascertain the contribution of non-oxidative bactericidial factors to the death and lysis of tolerant staphylococci. With these baseline data from normal granulocytes, we will then include white cells from patients with recurrent, superficial staphylococcal infections and with acute staphylococcal infections to ascertain which of several potentially important granulocytic bactericidal mechanisms is most important in eradicating phagocytized S. aureus strains. This information is expected to materially enhance the clinical management and survival of patients with staphylococcal bacteremia.